1. Field of the Invention
This invention relates to improved aqueous gelling and foaming acidizing compositions useful in oil and gas wells. More specifically, the invention relates to a method for increasing the efficacy of an ethoxylated fatty amine as a gelling agent for acid fracturing and stimulation of hydrocarbon bearing formations.
2. Description of the Prior Art
The basic concept of acidizing and/or hydraulically fracturing a subterranean well formation with an aqueous solution is an accepted commercial practice in the oil and gas production industry. Typically, in an acidizing treatment, the aqueous acid solution is introduced into the well and forced under pressure into the hydrocarbon producing formation so that the acid can react with the rock matrix or the like enlarging the pore spaces, thus increasing the formation permeability and hydrocarbon production rate. In the hydraulic acid fracturing procedures, fractures are produced in the formation at ultrahigh pressures and the acid solutions are introduced into the fractures to react with the flow channels, thus again enlarging the pore spaces and increasing the permeability in the fracture face and the surrounding formation.
It is also generally known to increase the viscosity of the aqueous acid solution being employed in acidizing and/ or fracture jobs such as to retard the acid reaction (decrease mobility of acid) and allow more time to achieve deeper penetration of the unreacted acid into the earth formation.
Thus, it is known to add various gelling agents to aqueous acid, producing a gelatinous aqueous acid media that prevents the acid from prematurely reacting with the formation.
Previously known gelling agents such as hydratable gums and cellulose derivatives have been used, but for the most part, have limited stability towards acid hydrolysis and are ineffective at elevated temperatures. Other high molecular weight polymeric gelling agents frequently exhibit shear instability, thus tend to degrade from high shear encountered in pumps, tubing and perforations in the wellbore during injection of the acidizing fluid. Such gelling agents are often difficult to disperse and usually require considerable mixing or agitation to develop full viscosity.
More recently, certain viscoelastic surfactant gelling agents which simultaneously act as foaming agents have been utilized in well stimulation treatments, such as fracture acidizing procedures and the like. Such viscoelastic surfactants do not degrade molecularly when subjected to shear, are simple to prepare, exhibit excellent viscosity as well as good fluid loss characteristics. In U.S. Pat. 4,324,669 and British Pat. No. 2,012,830 viscoelastic surfactant compositions based on certain water soluble organic solvents in combination with mixtures of ethoxylated fatty amines are disclosed as foaming/gelling agents for aqueous acids. However, viscoelastic surfactants usually require higher concentrations of surfactant than the polymeric gelling agent systems to develop equivalent viscosity. The present invention is viewed as an improvement in the foaming/gelling agents of these references.